The invention relates to an apparatus for the variable setting of control times of gas-exchange valves of an internal combustion engine with a drive element, a driven element, at least one pressure chamber, a pressurized medium system, and a pressure storage system, wherein the pressure chamber and the pressure storage system communicate with the pressurized medium system, wherein a phase position between the driven element and the drive element can be changed through the supply of pressurized medium to or the discharge of pressurized medium from the pressure chamber via the pressurized medium system.
In modern internal combustion engines, apparatuses for the variable setting of control times of gas-exchange valves are used to be able to variably shape the phase relation between the crankshaft and camshaft in a defined angular range, between a maximum advanced and a maximum retarded position. For this purpose, the device is integrated into a drive train, by which torque is transmitted from the crankshaft to the camshaft. This drive train can be realized, for example, as a belt, chain, or gearwheel drive.
Such a device is known, for example, from EP 1 025 343 B1. The apparatus comprises two rotors that can rotate relative to each other, wherein an outer rotor is in driven connection with the crankshaft and the inner rotor is locked in rotation with the camshaft. The apparatus comprises several pressure spaces, wherein each of the pressure spaces is divided by a vane into two counteracting pressure chambers. Through the supply of pressurized medium to or the discharge of pressurized medium from the pressure chambers, the vanes are shifted within the pressure spaces, which generates a targeted rotation of the rotors relative to each other and thus the camshaft relative to the crankshaft.
The supply of pressurized medium to or the discharge of pressure from the pressure chambers is controlled by a pressurized medium system, which comprises a pressurized medium pump, a tank, a control valve, and several pressurized medium lines. Here, a pressurized medium line connects the pressurized medium pump to the control valve. Each pressurized medium line connects one of the working connections of the control valve to the pressure chambers.
To guarantee the function of the apparatus, the pressure in the pressurized medium system must exceed a certain value in each operating phase of the internal combustion engine. This is especially critical in the idling phases of the internal combustion engine, because the pressurized medium pump is driven by the crankshaft and thus the system pressure increases with the rotational speed of the internal combustion engine. The system pressure provided by the pressurized medium pump is furthermore dependent on the pressurized medium temperature, wherein the system pressure decreases for increasing temperature. Thus, the pressurized medium pump must be designed such that this makes available sufficient system pressure under the least favorable conditions, in order to guarantee adjustment of the phase position of the inner rotor relative to the outer rotor.
If, during an idling phase of the internal combustion engine, an adjustment request is made on the device, then at the beginning of the adjustment process, the system pressure falls further due to the higher pressurized medium need. This can have the result that the adjustment process can be performed only with an adjustment speed that is too low. Thus, the performance of the internal combustion engine is reduced, wherein it can produce, for example, losses in the provided torque and increased raw-material emissions.
In addition, in U.S. Pat. No. 5,775,279, another such device is disclosed, in which a pressure storage device is provided, which communicates with a pressurized medium line, which connects the pressurized medium pump to the control valve. This pressure storage device is used to move the inner rotor relative to the outer rotor against the alternating and dragging moments of the camshaft into a base position when the internal combustion engine is turned off. This adjustment, which is to be performed just by the pressurized medium stored in the pressure storage device, requires a high pressure in the pressure storage device. The pressure storage device is consequently designed in such a way that the pressure, at which the pressure storage device is completely full, is significantly above the pressure that prevails during the idling of the internal combustion engine in the pressurized medium system. If the rpm's of the internal combustion engine decrease, then the pressure storage device empties before the idling rotational speed is reached. Thus, the pressurized medium volume that is available and that can be retrieved in the idling phase, is too low to guarantee an adjustment into these phases.